1. Field of the Invention The present invention relates to information handling systems, and more particularly to systems for processing image data for presentation on a display terminal, printer, or similar output device.
2. Description of Related Art
Image display systems have been developed to display digital images captured through optical scanning, video camera input, or via image sensors. The most basic image display systems simply reproduce the image stored in the digital image memory. More advanced systems allow for the transformation of the stored image through color enhancement, magnification (zoom), rotation, or other transformation.
The implementation of image magnification or zoom has been typically accomplished in the prior art through the use of pixel replication. In a system that uses pixel replication, an image to be magnified by a factor of 2 will be created by displaying two pixels of a given value for every one pixel of that value stored in the image storage. This form of magnification has the affect of creating what amounts to a single large pixel in place of each original pixel. At greater magnification factors this leads to considerable jaggedness in the outline of the image. Pixel replication is particularly undesirable in an image display system which allows for the display of multiple shades of gray or colors. In these systems, the replication of individual pixels creates a grainy picture of low quality.
Theoretical techniques exist for interpolating the color or intensity (gray shade) of the pixels of magnified images. The magnification process results in more than one pixel being displayed for every pixel of data stored. The addition of a pixel between a white pixel and a black pixel is better represented by a gray pixel than by the replication of either the black or white pixel. The implementation of these interpolation techniques, however, has not proved to be practical due to the considerable calculations required to interpolate the multitude of pixels in a display image. When implemented in software, interpolation results in unacceptably slow response times to magnification requests.
Tabata et al., "High Speed Image Scaling for Integrated Document Management" ACM Conference on Office Information Systems, Toronto, June 1984, discuss the use of high speed scaling techniques relying on table lookup and shift operations. The suggested techniques speed the process but still require the building and referencing of a table. Tabata et al. interpolate based on a subdivision that has an interval related to the numerator of the magnification factor. This causes a loss of efficiency when fine resolution on the magnification factor is required. In addition, the Tabata et al. technique is based on the period of the interpolated sample deviation to input intersample distance, which tends to have a long period further decreasing efficiency.